96 research outputs found
A complete study of the precision of the concentric MacLaurin spheroid method to calculate Jupiter's gravitational moments
This is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this recordA few years ago, Hubbard (2012, 2013) presented an elegant, non-perturbative method, called concentric MacLaurin spheroid (CMS), to calculate with very high accuracy the gravitational moments of a rotating fluid body following a barotropic pressure-density relationship. Having such an accurate method is of great importance for taking full advantage of the Juno mission, and its extremely precise determination of Jupiter gravitational moments, to better constrain the internal structure of the planet. Recently, several authors have applied this method to the Juno mission with 512 spheroids linearly spaced in altitude. We demonstrate in this paper that such calculations lead to errors larger than Juno's error bars, invalidating the aforederived Jupiter models at the level required by Juno's precision. We show that, in order to fulfill Juno's observational constraints, at least 1500 spheroids must be used with a cubic, square or exponential repartition, the most reliable solutions. When using a realistic equation of state instead of a polytrope, we highlight the necessity to properly describe the outermost layers to derive an accurate boundary condition, excluding in particular a zero pressure outer condition. Providing all these constraints are fulfilled, the CMS method can indeed be used to derive Jupiter models within Juno's present observational constraints. However, we show that the treatment of the outermost layers leads to irreducible errors in the calculation of the gravitational moments and thus on the inferred physical quantities for the planet. We have quantified these errors and evaluated the maximum precision that can be reached with the CMS method in the present and future exploitation of Juno's data
Impact of a new H/He equation of state on the evolution of massive brown dwarfs. New determination of the hydrogen burning limit
We have explored the impact of the latest equation of state (EOS) for dense
hydrogen-helium mixtures (Chabrier \& Debras 2021), which takes into account
the interactions between hydrogen and helium species, upon the evolution of
very low mass stars and brown dwarfs (BD). These interactions modify the
thermodynamic properties of the H/He mixture, notably the entropy, a quantity
of prime importance for these fully convective bodies, but also the onset and
the development of degeneracy throughout the body. This translates into a
faster cooling rate, i.e. cooler isentropes for a given mass and age, and thus
larger brown dwarf masses and smaller radii for given effective temperature and
luminosity than the models based on previous EOSs. This means that objects of a
given mass and age, in the range M\lesssim 0.1\,\msol, yr,
will have cooler effective temperatures and fainter luminosities. Confronting
these new models with several observationally determined BD dynamical masses,
we show that this improves the agreement between evolutionary models and
observations and resolves at least part of the observed discrepancies between
the properties of dynamical mass determinations and evolutionary models. A
noticeable consequence of this improvement of the dense H/He EOS is that it
yields a larger H-burning minimum mass, now found to be 0.075\,\msol
(78.5\,\mjup) with the ATMO atmosphere models for solar metallicity. These
updated brown dwarf models are made publicly available.Comment: To appear in Astronomy & Astrophysic
The acceleration of superrotation in simulated hot Jupiter atmospheres
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordContext. Atmospheric superrotating flows at the equator are a nearly ubiquitous result when conducting simulations of hot Jupiters.
One theory explaining how this zonally-coherent flow reaches equilibrium has already been developed in the literature. This understanding, however, relies on the existence of either an initial superrotating flow or a sheared flow, coupled with a slow evolution that
permits a linear steady state to be reached.
Aims. A consistent physical understanding of superrotation is needed for arbitrary drag and radiative timescales, along with the
relevance of taking linear steady states into account, needs to be assessed.
Methods. We obtained an analytical expression for the structure, frequency, and decay rate of propagating waves in hot Jupiter
atmospheres around a state at rest in the 2D shallow-water β–plane limit. We solved this expression numerically and confirmed the
robustness of our results with a 3D linear wave algorithm. We then compared it with 3D simulations of hot Jupiter atmospheres and
studied the nonlinear momentum fluxes.
Results. We show that under strong day-night heating, the dynamics do not transit through a linear steady state when starting from an
initial atmosphere in solid body rotation. We further demonstrate that non–linear effects favor the initial spin-up of superrotation and
that acceleration due to the vertical component of the eddy–momentum flux is critical to the initial development of superrotation .
Conclusions. We describe the initial phases of the acceleration of superrotation, including the consideration of differing radiative
and drag timescales, and we conclude that eddy-momentum-driven superrotating equatorial jets are robust, physical phenomena in
simulations of hot Jupiter atmospheres.Leverhulme TrustScience and Technology Facilities Counci
: a data-driven approach to correct for systematics in RV data -- Application to SPIRou data of the planet-hosting M dwarf GJ 251
Context: Recent advances in the development of precise radial velocity (RV)
instruments in the near-infrared (nIR) domain, such as SPIRou, have facilitated
the study of M-type stars to more effectively characterize planetary systems.
However, the nIR presents unique challenges in exoplanet detection due to
various sources of planet-independent signals which can result in systematic
errors in the RV data.
Aims: In order to address the challenges posed by the detection of
exoplanetary systems around M-type stars using nIR observations, we introduce a
new data-driven approach for correcting systematic errors in RV data. The
effectiveness of this method is demonstrated through its application to the
star GJ 251.
Methods: Our proposed method, referred to as (Weighted
principAl comPonent analysIs reconsTructIon), uses a dataset of per-line RV
time-series generated by the line-by-line (LBL) algorithm and employs a
weighted principal component analysis (wPCA) to reconstruct the original RV
time-series. A multi-step process is employed to determine the appropriate
number of components, with the ultimate goal of subtracting the wPCA
reconstruction of the per-line RV time-series from the original data in order
to correct systematic errors.
Results: The application of to GJ 251 successfully
eliminates spurious signals from the RV time-series and enables the first
detection in the nIR of GJ 251b, a known temperate super-Earth with an orbital
period of 14.2 days. This demonstrates that, even when systematics in SPIRou
data are unidentified, it is still possible to effectively address them and
fully realize the instrument's capability for exoplanet detection.
Additionally, in contrast to the use of optical RVs, this detection did not
require to filter out stellar activity, highlighting a key advantage of nIR RV
measurements.Comment: Submitted to A&A. For the publicly available Wapiti code, see
https://github.com/HkmMerwan/wapit
First-trimester cesarean scar pregnancy: a comparative analysis of treatment options from the international registry
Background: A cesarean scar pregnancy is an iatrogenic consequence of a previous cesarean delivery. The gestational sac implants into a niche created by the incision of the previous cesarean delivery, and this carries a substantial risk for major maternal complications. The aim of this study was to report, analyze, and compare the effectiveness and safety of different treatments options for cesarean scar pregnancies managed in the first trimester through a registry. Objective: This study aimed to evaluated the ultrasound findings, disease behavior, and management of first-trimester cesarean scar pregnancies. Study design: We created an international registry of cesarean scar pregnancy cases to study the ultrasound findings, disease behavior, and management of cesarean scar pregnancies. The Cesarean Scar Pregnancy Registry collects anonymized ultrasound and clinical data of individual patients with a cesarean scar pregnancy on a secure, digital information platform. Cases were uploaded by 31 participating centers across 19 countries. In this study, we only included live and failing cesarean scar pregnancies (with or without a positive fetal heart beat) that received active treatment (medical or surgical) before 12+6 weeks' gestation to evaluate the effectiveness and safety of the different management options. Patients managed expectantly were not included in this study and will be reported separately. Treatment was classified as successful if it led to a complete resolution of the pregnancy without the need for any additional medical interventions. Results: Between August 29, 2018, and February 28, 2023, we recorded 460 patients with cesarean scar pregnancies (281 live, 179 failing cesarean scar pregnancy) who fulfilled the inclusion criteria and were registered. A total of 270 of 460 (58.7%) patients were managed surgically, 123 of 460 (26.7%) patients underwent medical management, 46 of 460 (10%) patients underwent balloon management, and 21 of 460 (4.6%) patients received other, less frequently used treatment options. Suction evacuation was very effective with a success rate of 202 of 221 (91.5%; 95% confidence interval, 87.8-95.2), whereas systemic methotrexate was least effective with only 38 of 64 (59.4%; 95% confidence interval, 48.4-70.4) patients not requiring additional treatment. Overall, surgical treatment of cesarean scar pregnancies was successful in 236 of 258 (91.5%, 95% confidence interval, 88.4-94.5) patients and complications were observed in 24 of 258 patients (9.3%; 95% confidence interval, 6.6-11.9). Conclusion: A cesarean scar pregnancy can be managed effectively in the first trimester of pregnancy in more than 90% of cases with either suction evacuation, balloon treatment, or surgical excision. The effectiveness of all treatment options decreases with advancing gestational age, and cesarean scar pregnancies should be treated as early as possible after confirmation of the diagnosis. Local medical treatment with potassium chloride or methotrexate is less efficient and has higher rates of complications than the other treatment options. Systemic methotrexate has a substantial risk of failing and a higher complication rate and should not be recommended as first-line treatment
Ground-breaking Exoplanet Science with the ANDES spectrograph at the ELT
In the past decade the study of exoplanet atmospheres at high-spectral
resolution, via transmission/emission spectroscopy and cross-correlation
techniques for atomic/molecular mapping, has become a powerful and consolidated
methodology. The current limitation is the signal-to-noise ratio during a
planetary transit. This limitation will be overcome by ANDES, an optical and
near-infrared high-resolution spectrograph for the ELT. ANDES will be a
powerful transformational instrument for exoplanet science. It will enable the
study of giant planet atmospheres, allowing not only an exquisite determination
of atmospheric composition, but also the study of isotopic compositions,
dynamics and weather patterns, mapping the planetary atmospheres and probing
atmospheric formation and evolution models. The unprecedented angular
resolution of ANDES, will also allow us to explore the initial conditions in
which planets form in proto-planetary disks. The main science case of ANDES,
however, is the study of small, rocky exoplanet atmospheres, including the
potential for biomarker detections, and the ability to reach this science case
is driving its instrumental design. Here we discuss our simulations and the
observing strategies to achieve this specific science goal. Since ANDES will be
operational at the same time as NASA's JWST and ESA's ARIEL missions, it will
provide enormous synergies in the characterization of planetary atmospheres at
high and low spectral resolution. Moreover, ANDES will be able to probe for the
first time the atmospheres of several giant and small planets in reflected
light. In particular, we show how ANDES will be able to unlock the reflected
light atmospheric signal of a golden sample of nearby non-transiting habitable
zone earth-sized planets within a few tenths of nights, a scientific objective
that no other currently approved astronomical facility will be able to reach.Comment: 66 pages (103 with references) 20 figures. Submitted to Experimental
Astronom
ANDES, the high resolution spectrograph for the ELT: science case, baseline design and path to construction
Prognostic factors in prostate cancer
Prognostic factors in organ confined prostate cancer will reflect survival after surgical radical prostatectomy. Gleason score, tumour volume, surgical margins and Ki-67 index have the most significant prognosticators. Also the origins from the transitional zone, p53 status in cancer tissue, stage, and aneuploidy have shown prognostic significance. Progression-associated features include Gleason score, stage, and capsular invasion, but PSA is also highly significant. Progression can also be predicted with biological markers (E-cadherin, microvessel density, and aneuploidy) with high level of significance. Other prognostic features of clinical or PSA-associated progression include age, IGF-1, p27, and Ki-67. In patients who were treated with radiotherapy the survival was potentially predictable with age, race and p53, but available research on other markers is limited. The most significant published survival-associated prognosticators of prostate cancer with extension outside prostate are microvessel density and total blood PSA. However, survival can potentially be predicted by other markers like androgen receptor, and Ki-67-positive cell fraction. In advanced prostate cancer nuclear morphometry and Gleason score are the most highly significant progression-associated prognosticators. In conclusion, Gleason score, capsular invasion, blood PSA, stage, and aneuploidy are the best markers of progression in organ confined disease. Other biological markers are less important. In advanced disease Gleason score and nuclear morphometry can be used as predictors of progression. Compound prognostic factors based on combinations of single prognosticators, or on gene expression profiles (tested by DNA arrays) are promising, but clinically relevant data is still lacking
- …